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Worksheet 07 Key

# Worksheet 07 Key - CH 302 Spring 2007 Worksheet 7 For all...

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CH 302 Spring 2007 Worksheet 7 For all of the problems on this worksheet, use the following K values: H 3 PO 4 : pK a1 = 2 pK a2 = 6 pK a3 = 10 H 2 CO 3 : pK a1 = 4 pK a2 = 10 1. You drop 0.1 mol of HI into 1 L of water. What is the pH of solution? Answer: pH = -log[H + ] = -log(C a ) = 1 2. You drop 0.1 mol of KOH into a 1 L solution of 1 M H 3 PO 4 and KH 2 PO 4 . What is the pH of the solution? Answer: Neutralize; you have 0.9 M H 3 A and 1.1 M H 2 A - . [H + ] = K a1 (C a /C b ) = 10 -2 (0.9/1.1) = 8.18 x 10 -3 pH = 2.09 3. You drop 0.1 mol of NaOH into a 1 L solution of 0.5 M RbHCO 3 and 0.5 M Na 2 CO 3 . What is the pH of the solution? Answer: Neutralize; you have 0.4 M HA 2- and 0.6 M A 3- . [H + ] = K a3 (C a /C b ) = 10 -10 (0.4/0.6) = 6.67 x 10 -11 pH = 10.18 4. You drop 0.5 mol of NaOH into a 1 L solution of 0.5 M RbHCO 3 and 0.5 M Na 2 CO 3 . What is the pH of the solution? Answer: Neutralize; you have 1.0 M A2-. [OH - ] = (K b1 C b )1/2 = [(K w /K a2 )C b ) 1/2 = (10 -4 x 1.0) 1/2 = 10 -2 pOH = 2 pH = 12 5. You drop 1.5 mol of NaOH into a 1 L solution of 0.5 M RbHCO 3 and 0.5 M Na 2 CO 3 . What is the pH of the solution? Answer: Neutralize; you have 1.0 M A 2- and 1.0 M OH - . [OH - ] = C b = 1.0 M pOH = -1 pH = 15 For questions 6 through 13, 1.5 L 0.1 M H 3 PO 4 is titrated with 1 M NaOH. Give the pH for the given amount of NaOH solution added to the H 3 PO 4 solution.

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